Particle number fluctuations in nuclear collisions within an excluded volume hadron gas model

Multiplicity fluctuations are studied in the van der Waals excluded volume hadron-resonance gas model. The calculations are done in the grand canonical ensemble within the Boltzmann statistics approximation. The scaled variances for positive, negative, and all charged hadrons are calculated along the chemical freeze-out line of nucleus-nucleus collisions at different collision energies. The multiplicity fluctuations are found to be suppressed in the van der Waals gas. The numerical calculations are presented for two values of the hard-core hadron radius, r=0.3 and 0.5 fm, as well as for the upper limit of the excluded volume suppression effects